An internal combustion engine with an exhaust gas after-treatment system comprising a selective catalytic reducer (SCR) catalyst is commonly used to treat NOx emissions. A reductant, often aqueous urea, is injected via a dosing device in the exhaust line upstream of the SCR catalyst. The NOx reacts with the reductant to form byproducts such as water and nitrogen.
One example approach positions the dosing device upstream of the SCR catalyst in an exhaust bypass line. A control valve is positioned in the exhaust bypass line to control the volume flow of exhaust through the bypass line to control the temperature of the hydrolysis catalyst. Another example approach is to use HC enrichment by introducing unburned hydrocarbons directly into the exhaust-gas discharge system to act as the reductant by means of post-injection of additional fuel into a combustion chamber.
A potential issue noted by the inventors with the use of a control valve in the exhaust bypass line is the relative complexity of the system and the temperature control and selected mass flow limitations of using a valve positioned in the exhaust bypass line. Further, there may be operating conditions under which reductant may not be delivered to the SCR catalyst and allow the release of NOx. Another potential issue noted by the inventors is with HC enrichment which utilizes post-injection. The internal combustion engine may be susceptible to thinning or contamination of the oil with unburned hydrocarbons. Further, additional fuel is used as the reducing agent thereby increasing overall fuel consumption.
One potential approach to at least partially address some of the above issues includes an internal combustion engine comprising an intake system for the supply of charge air and an exhaust gas discharge system for the discharge of the exhaust gases. Further at least one selective catalytic converter is arranged in the exhaust gas discharge system for the reduction of nitrogen oxides wherein an oxidation catalytic converter being arranged as a further exhaust gas after-treatment system upstream of the at least one selective catalytic converter. A bypass line branching off from the intake system and issuing air into the exhaust gas discharge system between the oxidation catalytic converter and the at least one selective catalytic converter further comprising a dosing device being provided for introducing liquid urea as a reducing agent for the at least one selective catalytic converter into the bypass line.
Another potential approach to at least partially address some of the above issues includes a method for operating an internal combustion engine having a control element for the adjustment of the air flow rate conducted through the bypass line wherein the bypass line is opened in order to supply ammonia as the reducing agent to the at least one selective catalytic converter.
Another potential approach includes a method for controlling an engine with a selective catalytic reducer coupled to the engine exhaust comprising supplying compressed air to the engine to achieve a selected torque and injecting a reductant into the SCR. The temperature of the reductant may be controlled within a predetermined range by portioning an air flow into said reductant between a portion of said compressed air and ambient air. Further, the engine torque may be adjusted to compensate for said portioning of said compressed air.
Another potential approach further includes a method for maintaining temperature of the dosing device within a selected range, while maintaining emissions control and operating the engine at a selected power output. The method comprises supplying compressed air to the engine to achieve a selected torque, injecting a reductant into the selective catalytic converter, and controlling temperature of the reductant within a predetermined range by portioning an air flow into the reductant between a portion of the compressed air and ambient air. The method may further adjust engine torque to compensate for the portioning of the compressed air. The compressed air may be supplied from a compressor driven by a turbine positioned in the engine exhaust discharge system.
In another approach, a structure and method which provides for controlling temperature of a reductant dosing device by combining both portioning of air between a compressor and ambient air, and also portioning exhaust flow between exhaust upstream and downstream of a turbine. An advantage of this approach is that a greater range of temperature control is achieved with fewer disturbances to engine torque, and various such disturbances may be more easily corrected. In a particular example, the method comprises: supplying compressed air to an engine from a compressor driven by a turbine coupled to exhaust from the engine; injecting a reductant into a catalyst coupled to the exhaust; and controlling temperature of the reductant to be within a predetermined range by passing over the reductant one or more of the following: a combination of compressed air and ambient air; or, a combination of the exhaust upstream and downstream of the turbine.
In another example, a method is described for controlling an engine having a turbocharger with a turbine positioned in the engine exhaust, a Selective Catalytic Reducer (SCR) catalyst positioned downstream of the turbine, and a compressor driven by the turbine, comprising: supplying compressed air from the compressor to the engine to achieve a desired torque; injecting a urea reductant into the SCR through a dosing device to reduce NOx; controlling temperature of the device to be within a predetermined range for conversion of the urea to ammonia by one or more of the following: portioning an air flow across the dosing device between a portion of the compressed air and another portion of ambient air; or, portioning an exhaust flow across the dosing device between a portion of the exhaust upstream and downstream of the turbine; adjusting engine torque to compensate for the portioning of the compressed air; and when the portioning airflow is used for the temperature control and the engine torque adjusting reaches a threshold, then change from the portioning airflow to the portioning exhaust flow for the temperature control. In a further example, changing from the portioning exhaust flow for the temperature control to the portioning airflow for the temperature control when the portioning exhaust flow is used for the temperature control and the engine torque adjusting reaches said threshold.
By choosing between the two mechanisms to control temperature of the dosing device to a predetermined temperature, portioning airflow or portioning exhaust flow, a wider range of temperature control may be achieved. Further, torque disturbances that may be caused by diverting a portion of the compressed air or a portion of the exhaust upstream of the turbine, may be corrected or avoided.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.